"I wonder if dji tested the app before releasing it to he public"... laughable, didn't you know we're official alpha testers for dji? Hah.
Lag wise, I see a lot of it when I first fire up the app, regardless of the device being used (I have a total of 4 to choose from, up to a 10.1" tab4). All is usually takes is backing out of the app, killing it (along with all other tasks) in task manager, then re-launching the app.
For whatever reason, this usually drops my lag below 250ms or so, which is about as real time as it gets without inviting bill mahar over. At most, I've had to repeat the procedure twice, but it usually does the trick after the first attempt. Give it a try and see if it doesn't atleast make a difference. (I'm guessing ram loading?)